1. Field of the Invention
This invention relates to a light beam scanning read-out apparatus and a light beam scanning recording apparatus. This invention particularly relates to a light beam scanning read-out apparatus and a light beam scanning recording apparatus wherein light beam scanning is conducted by generating surface acoustic waves in an optical waveguide and deflecting the guided optical wave by the diffracting action of the surface acoustic waves.
2. Description of the Prior Art
There have heretofore been used widely light beam scanning read-out apparatuses wherein an image recorded on a read-out original is read out by scanning the read-out original with a light beam and photoelectrically detecting light transmitting through the read-out original, light reflected thereby, or light emitted thereby, and light beam scanning recording apparatuses for scanning a light-sensitive material with a light beam and recording a continuous tone or black-and-white two-valued image on the light-sensitive material. As the light beam scanning apparatuses for one-dimensionally scanning the reading light beam or the recording light beam in the light beam scanning read-out apparatuses and the light beam scanning recording apparatuses, those as described below are known.
(1) Apparatuses wherein the light beam is deflected and scanned by a mechanical type light deflector such as a galvanometer mirror or a polygon mirror (multi-face rotating mirror).
(2) Apparatuses wherein the light beam is deflected and scanned by a light deflector using solid-state light deflecting device, such as an EOD (electro-optic deflector) or an AOD (acousto-optic deflector).
(3) Apparatuses wherein a shutter array such as a liquid crystal device array or a PLZT array is combined with a linear light source, and the shutter devices of the shutter array are independently connected to drive circuits and turned on and off in accordance with an image signal to conduct linear sequential scanning.
(4) Apparatuses wherein many light emitting devices such as LEDs are arrayed in a line, independently connected to drive circuits, and turned on and off in accordance with an image signal to carry out linear sequential scanning.
The light beam scanning apparatuses described in (1) have the drawbacks that the mechanical type light deflector is easily affected by vibration, exhibits low mechanical durability, and requires troublesome adjustments. Further, a large optical system is necessary for swinging and deflecting the light beam, and the read-out apparatuses and the recording apparatuses become large.
The light beam scanning apparatuses described in (2) and using the EOD or AOD have the same drawback that the apparatuses for swinging and deflecting the light beam become large. Particularly, since the light deflection angle cannot be adjusted to be large with the EOD and the AOD, the optical system becomes larger than in the case where the mechanical light deflector is used as described in (1).
In the light beam scanning apparatuses using the shutter array as described in (3), since two polarizing plates must be used, the light utilization efficiency of the light source is very low.
The light beam scanning apparatuses using many light emitting devices arrayed in a line as described in (4) have the drawback that, since fluctuations arise in light emission intensity among the light emitting devices, the apparatuses are not suitable for accurate scanning.
Accordingly, it has been proposed to constitute a light beam scanning apparatus so that guided optical wave advancing inside of an optical waveguide is deflected by surface acoustic waves (SAW), and a light beam is scanned by changing the angle of deflection. The light beam scanning apparatus comprises:
(i) an optical waveguide formed of a material allowing propagation of surface acoustic waves therethrough,
(ii) a light source for emitting light into said optical waveguide,
(iii) an optical system for converting the guided optical wave advancing inside of the optical waveguide into collimated optical guided wave,
(iv) a means for generating the surface acoustic waves, which advance in a direction intersecting the optical path of the guided optical wave and deflect the guided optical wave, in the optical waveguide, and
(v) a drive circuit for operating the surface acoustic wave generating means so that it generates the surface acoustic waves the frequency of which changes continuously. The light beam scanning read-out apparatus and the light beam scanning recording apparatus wherein said light beam scanning apparatus is used exhibit high durability, high resistance to vibration and a high light utilization efficiency, are easy to adjust and suitable for accurate scanning, and can be made small to some extent.
However, in the light beam scanning read-out apparatus and the light beam scanning recording apparatus wherein the aforesaid light beam scanning apparatus is used, since an optical device such as a prism coupler is provided for emitting the guided and deflected optical wave out of the optical waveguide and a converging lens is provided for converging the scanning light, which is emitted out of the optical waveguide, on a read-out original or a light-sensitive material, the sizes of the read-out apparatus and the recording apparatus cannot be made substantially small. Also, deflection of the guided optical wave is caused by Bragg diffraction from the acousto-optic interaction between the guided optical wave and the surface acoustic waves. However, in such light deflection, the deflection angle cannot be adjusted to be large, and therefore the distance between the optical waveguide and the read-out original or the light-sensitive material must be adjusted to be long in order to adjust the light beam scanning width to a large value. As a result, the light beam scanning read-out apparatus and the light beam scanning recording apparatus become large.
Also, in the case where the prism coupler is used, the gap between the prism bottom surface and the optical waveguide must be adjusted accurately, and an expensive fine adjustment mechanism is required for this purpose. The prism coupler is also expensive. Therefore, the light beam scanning read-out apparatus and the light beam scanning recording apparatus become expensive.
Further, besides the aforesaid adjustment work, accurate adjustment of the position of the converging lens with respect to the position of the optical waveguide is necessary. Thus the light beam scanning read-out apparatus and the light beam scanning recording apparatus wherein the aforesaid light beam scanning apparatus is used require very troublesome adjustments. Also, since many adjustments are necessary, the reliability of the light beam scanning read-out apparatus and the light beam scanning recording apparatus of this type is low.
Also, when the guided optical wave is emitted out of the optical waveguide by use of the prism coupler, in shape the emitted light becomes a parallel group of rays in a direction parallel to the prism bottom ridge and becomes a divergent group of rays in a direction normal thereto. Therefore, in order to converge the scanning light into a circular spot, it is necessary to use a special converging lens instead of ordinary spherical lenses.
Further, in the case where the prism coupler and the converging lens are used, when a defect arises with these optical devices or the end face of the optical waveguide, the shape of the scanning light beam spot is adversely affected. Particularly, in the case where the guided optical wave is emitted out of the end face of the optical waveguide, a defect at the end face directly leads to a defect of the scanning light beam spot, and it thus becomes impossible to achieve accurate scanning.